Symptoms of a Bad ECM (And What You Should Do)


Every now and then a part or component fails in a way that the company makes a recall. The rest of the time it is up to the owner to figure out when something goes wrong.

Engine control modules weren't always an essential component of a vehicle, obviously. Since the 1970s the modules have become increasingly integral to the operation of a vehicle.

Now, a bad ECM can cause rolling damage or prevent a vehicle from operating at all. Learning to spot the warning signs of an ECM on the decline can save you time and money on repairs and replacements.

To find the most common symptoms that indicate an ECM is going bad, read on. Pretty sure that the ECM's shot? We'll also tell you what can be done with a bad ECM.

Understanding the ECM

Engine Control Modules interact with sensors throughout the vehicle to make changes to engine systems. Sometimes referred to as the 'brain' of the engine, and also known as the Engine Control Unite (ECU) or even as the Powertrain Control Module(PCM) this critical component of modern vehicles streamlines processes.

When sensors relay information, the ECM makes decisions on engine spark tuning and fuel usage. These changes give peak performance under different conditions and count external and internal temperatures variables. The goal, for the ECM, is to work seamlessly under each situation which increases the longevity of engine components by avoiding strain or underutilization.

More specifically, the ECM regulates and monitors systems such as the throttle position through a sensor. This information is used to determine the air and fuel mixture to create the right amount of power to maintain speed.

Bad ECM Dangers

Since ECM controls so much of the way the engine functions, a bad ECM obviously can cause the very problem the ECM usually prevents. Wear on engine components accelerates, performance suffers, and noticeable gaps in power and fuel usage appear.

The longer the symptoms persist, the more damage the engine will accrue and the more expensive repairs will become, especially if damage exceeds repair thresholds and replacements become the only option.

All of the warning lights on the dash get lit from information provided by and processed through theECM and it sensor network. So a bad ECM will likely not even tell you where a problem is, or what problems are occurring. Fortunately, as you will find out, the vehicle is more likely to not even start when the ECM decays to that point, so an unreported engine overheat is far less likely.

Another danger comes from the regulation of the camshaft and crankshaft positioning. Sensors determine the position may deliver faulty information which will change up the engine cycles and airflow through the manifold. This may not result in an engine seizing or a crankshaft snapping, there are physical safeties for those.

Emissions regulation comes through the ECM and in states like California, a sudden loss of control for emissions could net you an expensive ticket.


These symptoms reflect problems occurring with a bad ECM. When caught in time these symptoms can be removed and the ECM saved. AS the damage and miscalibrations proliferate, components may break and more symptoms may appear.

Though some symptoms of a bad ECM may be more obvious or notable, that doesn't necessarily mean they will be more damaging. Some of the smaller and more subtle symptoms can reflect the larger dangers in terms of damage or part failure.

Take note that each of these symptoms can be caused by other parts either not working, or not working in conjunction. Since the ECM controls so many things, it can manifest problems in a lot of places. But what the ECM does is monitor and control other parts, so those parts going bad would produce some of the same symptoms.

Check Engine Light

We'll start with the least helpful symptom: the check engine light. Problems with the check engine light drive motorists and mechanics crazy. The light, though helpful in indicating the occurrence of an issue, doesn't provide particularly robust information.

Fortunately, along with the advances in ECMs diagnostic tools used by mechanics can find exact error codes that are being broadcast to isolate the issue. This doesn't help the average motorist to know why the light turned on, but it does shorten the diagnostic process.

The check engine light may turn on to show that sensors have become damaged or lost, it may also indicate that the ECM can no longer process information properly.

Engine Performance

For pattern seeking motorists and those who keep precise notes of their fuel and travel times, engine performance problems will quickly show the presence of a bad ECM.

Drops in fuel efficiency can only be caused by a few issues within the vehicle, so are easier to self-diagnose. (find others)

A vehicle that feels as if it is struggling to shift can show a problem with timing in the ECM or with the transmission. Again, this becomes an either/or situation which makes determining the root cause easy for drivers.

A subtle but noticeable variation in drive times between common destinations could show a loss of power and speed while changing grades on the road. This can also be due to tire pressure, which can be ruled out by routine checks of the tire psi.

Engine Stalls and Misfires

Unfortunately, patterns in engine stalls and misfires rarely exist. These issues may occur because of a variety of fluids, parts, or electrical components. While a bad ECM could be causing issues in telling the engine to do the wrong thing at the wrong time, that isn't always obvious.

Vehicle Not Starting

The worst issue a bad ECM causes (from a day to day perspective) makes the truck crank, but not start. This may be a once in a while issue or a near total bricking of the system where the vehicle becomes a very heavy paperweight.

In these instances, the ECM problems prevent engine operations from completing an ignition sequence.

Not starting can be a result of a shoddy alternator, bad battery, or broken ignition switch but these are also more easily testable variables.

Bad ECM Causes

Now that we've gone through the symptoms, let's take a closer look at what is going on with ECM failure. The following reflect damage and failures that lead to a bad ECM. Understanding these causes also gives you more tools for understanding the root cause of the above symptoms.

Physical Shock

While most of the following cover ways that electrical shock can happen to the ECM, physical shock also causes issues. An ECM that isn't seated well or has loose housing can rattle and allow the ECM to be physically shocked. Sudden stops and starts can cause components in a compromised housing to shift and break.

Fuel Solenoid

One of the main reasons an ECM fails comes from the electronic fuel solenoid. Shorts in the solenoid, often from corrosion or a wire running through the solenoid into the ECM.

Located on the fuel pump, the electronic fuel solenoid regulates fuel passing into the carburetor. When it locks down fuel can't transfer. When it fires with a wire in the wrong place, the shock can stun or fry the ECM.

Injector Wiring Harness

Corrosion and breaks in the wiring of the harness can produce shorts in the ECM. corrosion also works to make holes in the ECM wiring harness which allows exposure to other parts and weathering of elements.


Caused by caustic substance and moisture, corrosion causes lasting damage slowly. Most corrosion damage limits the lifespan of the ECM to 5-10 years. Corrosion may start in the wiring harness or a seal around the ECM component.

Water corrosion gets accelerated when working in high to low-temperature shifts. The moisture can freeze and create crystals which interfere with connections and push them apart. Heat rarely affects the ECM unless the housing has been compromised, where it can lead to melts.


Starter replacements, in particular, cause issues when bypassing override sensors becomes necessary to match parts or rebuilds together. The voltage spikes cause damage to the ECM over time and generate fault codes.

ECM symptoms noted after a starter replacement can be a coincidence but most likely is an issue with the starter replacement mismatch.


Poor grounding in the ECM or wiring around the ECM, especially those going to the battery, will create a problem. Grounding keeps the electrical discharge from building up in forms of static and charge. Latent, undirected electricity will do damage to any of the electronics, especially the ECM and its sensors.

Dead battery cells may cause issues with grounding by offering a place of incomplete charge and discharge to accumulate.

Jump Starts

A jump start where the cables get connected improperly may spike the ECM and cause a short. Different amps around the ECM may be damaged even if the ECM itself doesn't short, which makes it more likely a smaller shock will cause a short.

Bad ECM Solutions

Now that a bad ECM has been identified, the question is what do you do about it? Well, the leading option is simply replacing. ECM components designers made them to work together and tested them together. Pulling out any one part and putting something new in may fix the immediate issue, but will likely not last long.

Lingering damage or damage in putting the units back together cause as much potential for intrusion(through corrosion) and reinstalling into a harness puts the same dangers of shock and grounding back into play (depending on where the initial damage source started).


Repairs and reprogramming of an ECM both suffer from the same two problems. The first is that the cost to do so often outstrips buying a new one and having it installed. This is further complicated by the lack of peace of mind in a rebuilt or refurbished part.

The second issue comes from the technical know-how needed to do the repairs. Since the EECM is as much computer as a car part, it requires specialized knowledge to repair and work with. this is part of the reason the price to repair is high.

The other part of the expertise issue comes in the form of parts manufactured and tested to work together. Computer components, even the same make from the same brand, will not always work together properly. It is similar to organ transplants, where even the same family members don't always match well from variations in blood type and etc.

This makes repairs take time (to find the correct components) and they don't last as long (once the housing is opened nothing fits as well as when it was first assembled).

Timetables for a repair can be lengthy, as well. Repair cycle times differ for repairs, but the difficulty of part matching for ECM makes it one of the longest.


Replacing a bad ECM takes a lot less time and money. We can answer questions about the process and what components will work best for you or your mechanic. Replacement of an ECM comes with guarantees on the lifespan and warranty. Many dealerships prefer to go this route as well because it means less time and fewer repairs from them over time.

Getting back on the road means getting back to work. Sitting and waiting for repair cycle time adds stress to the wallet bleed. Replacement services ship in as little as a day and a max of 3, check out shipment policies for the best estimates.

Shop Good ECMs

Getting a good quality ECM makes a difference in needing to make any changes later on the line. Frequent and proper maintenance of the engine and sensors will keep the whole system running better, longer.

Shop all the best brands of ECM manufacturers such as Cummins and Caterpillar.

We offer comprehensive information on the products we sell so that you can ensure you get the right part for your needs. Whether you order for yourself or for a company, we make understanding the order simple and the timetables clear.

Posted On: 27/04/2018

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